The EChO spacecraft will have a launch mass of about 2.1 tons, and will be made up of two principle modules:

• the payload module, which includes the telescope assembly, the EChO science instrument and the fine guidance sensor (FGS) along with some of the support equipment;

• the service module, which provides the majority of the means and resources required to support the payload and to keep the spacecraft running during all mission phases.

The ESA reference design concept for the EChO mission. Concentric shields and baffles surround the telescope, and provide the high degree of thermal shielding needed to achieve a telescope operating temperature of around 45 Kelvin. Solar panels are accommodated on the Sun shield Credit: ESA

Payload Module

An ESA study carried out at the Concurrent Design Facility in ESTEC, the Netherlands, has provided a reference design concept for the primary payload elements: a simple Cassegrain telescope with a field-of-view of 20"x20", and a spectrometer covering the 0.4 – 11 micron waveband. This reference design will be studied further studied by ESA, while industry and instrument consortia will study and propose alternative designs over the next few months

Service Module

The service module handles all functions needed to operate the payload, including the telemetry, power systems, thermal control and the attitude and orbit control systems (AOCS).

High photometric stability is one of the most stringent requirements of the EChO mission, with a stability of 10^-4 (3 sigma) or better required over a time scale of about 10 hours. As a result, fine pointing stability relative to the host star is mandatory. This will be achieved with a combination of a fine guidance sensor (FGS) that uses a fraction of the signal from the optical channel, and fine AOCS actuators.